Conventional surgical techniques use ultraviolet light and short wavelength lasers to modify the shape of the cornea. For example, excimer lasers, such as those described in U.S. Pat. No. 4,840,175 to Peyman, which is incorporated herein by reference, emit pulsed ultraviolet radiation, which can be used to decompose or photoablate tissue in the live cornea to reshape the cornea.
Specifically, the Peyman patent discloses the laser surgical technique known as laser in situ keratomycosis (LASIK). In this technique, a portion of the front of the live cornea can be cut away in the form of a flap having a thickness of about 160 microns. This cut portion is moved away from the live cornea to expose an inner surface of the cornea. A laser beam is then directed onto the exposed inner surface to ablate a desired amount of the inner surface up to 150–180 microns deep. The cut portion is reattached over the ablated portion of the cornea and assumes a shape conforming to that of the ablated portion. The LASIK procedure is generally sufficient to correct myopia or distance vision. However, in many patients while the LASIK procedure is sufficient to correct distance vision it does not correct reading vision in patients who are presbyopic. Presbyopia is a condition which occurs after age 40 in which the lens of the eye loses its ability to change focus. When a distinctive object is in sharp focus on the retina, close objects are out of focus or blurred. To bring close objects into focus the lens of the eye changes shape to bring these objects into focus. This rapid movement of the lens occurs without conscience thought through and allows objects to be brought into focus. When the lens of the eye losses this ability, reading glasses or bifocal glasses are used. When a patient in their 40's and 50's have laser surgery and achieve corrected distance vision they still need glasses for reading. There are frequently 2 pairs needed one for intermediate distance, such as the computer and one for close reading vision.
Additional methods for correcting the refractive error in the eye include inserting an implant in between layers of the cornea. Generally, this is achieved using several different methods. The first method involves inserting a ring between layers of the cornea, as described in U.S. Pat. No. 5,405,384 to Silvestrini. Typically, a dissector is inserted in to the cornea to form a channel therein. Once the dissector is removed, a ring is then inserted into the channel to alter the curvature of the cornea. In the second method, a flap can be created similarly to the LASIK procedure, described above, and a large lens can be inserted under the flap to change the shape of the cornea, as described in U.S. Pat. No. 5,919,785 to Peyman and U.S. Pat. No. 6,102,946 to Nigam. The third method involves forming a pocket using a mechanical instrument, and inserting an implant into the pocket, as described in U.S. Pat. No. 4,655,774 to Choyce. These procedures all induce a single corneal curvature change and do not correct both distance vision and close vision in a bifocal or multifocal manner.
Additionally, even though these existing intracorneal lenses are somewhat suitable for correcting distant vision disorders, they typically cause the eye to experience an undesirable side effect commonly referred to as a “halo effect”, which is a ring of light that a person will see in the eye having an implanted intracorneal lens. A halo effect is caused due to light entering into or being refracted by the intracorneal lens at certain angles which creates a glare that is sensed by the retina of the eye and thus experienced by the person.
Although the severity of the halo effect can vary depending on the shape of the intracorneal lens and the amount of direct and ambient light being received by the eye, the halo effect can cause the patient much annoyance. Also, in certain instances, the halo effect can also adversely affect the patient's ability to read, drive a car and perform other routine activities requiring acute vision.
Additionally, many of these conventional techniques require relatively large lenses or corneal implants that stretch or expand the corneal surface to accommodate the intracorneal lens. These large lenses can lead to corneal erosion, which is generally caused by corneal cells dying since the lens does not allow nutrients to flow through portions of the cornea.
Accordingly, a need exists for intracorneal lenses, which can help correct the vision in the eye without displacing the corneal surface, while simultaneously eliminating or reducing glare and the halo effect due to light reflecting off of the intracorneal lens.